Directional drilling involves the practice of drilling non-vertical wells and is typically employed in oilfield directional drilling, utility installation directional drilling (horizontal directional drilling or directional boring), and surface-in-seam drilling, which horizontally intersects a vertical well target to extract coal bed methane.
Known directional drilling systems generally include a mud motor placed in the drill string to power a bit while drilling. A mud motor is a progressive cavity positive displacement pump that uses drilling fluid from the drill string to create eccentric motion in the power section of the motor (e.g., via turning a helical rotor). This motion is transferred as concentric power through a stator to the drill bit. As a result, the flow of fluid transmits power, allowing the assembly to rotate and turn the bit.
Mud motors can be configured to have a bend in them using different settings on the motor itself. Typical mud motors can be modified from 0 degrees to 4 degrees with several increments in deviation per degree of bend. The amount of bend is determined by a rate of climb or radius of curve needed to reach the target zone. By using a downhole measurement tool such as a measurement-while-drilling (MWD) tool or a logging-while-drilling (LWD) tool, a directional driller can receive and monitor guidance information and/or information regarding rock or sediment characterization in the borehole (e.g., borehole inclination, pressure, and/or gamma radiation counts) and steer the bit to the desired target zone.
Downhole measurement tools such as MWD/LWD tools (hereinafter “information subs”) are ordinarily located a considerable distance away from the bit/bore end when the mud motor is in use. Because downhole mud motors are generally not designed or equipped to incorporate information subs at the bit box where the bit attaches to the motor, the sub is often located at a trailing point on the mud motor or along the drill string, placing the information sub anywhere from ten to eighty-five feet above the bit/wellbore end. As a result, guidance and rock characterization information transmitted from the information sub is instructive regarding the location and rock conditions where the bit has previously travelled, not where it currently is. This lack of real-time information has been described as driving a car forward, while looking through the rear window. This information delay becomes problematic in instances where the bit veers of course. Before the driller detects a potential problem, the boring device has veered many feet off of an acceptable trajectory, risking costly and even dangerous mistakes should the bit encounter cable lines, gas lines, unfriendly rock characteristics, or the like.
Even in instances in which it is or could be possible to attach an information sub to the bit box of a downhole mud motor, current bit-to-bend lengths, or the distance between the bit attached to the mud motor and the bend in the mud motor, prevent proper steering. That is, the bit-to-bend lengths of existing downhole mud motors do not allow for modern planned drill trajectories or trajectories that take into account real-time borehole information to be achieved in the vertical, curved, and horizontal sections of the well bore.
As a result of the distant placement of information subs and extended “bit to bends,” drillers operate on delayed wellbore location and characterization knowledge and are unable to achieve desired wellbore trajectories or make informed, real-time decisions regarding maintaining and/or correcting wellbore paths.